About Length Units

The metric system uses the metre (m) as its base unit, defined since 1983 as the distance light travels in 1/299,792,458 of a second. The imperial system (feet, inches, miles) remains common in the US and UK for everyday distances. Nautical miles are used in aviation and maritime navigation.

Common Conversions

  • 1 inch = 2.54 cm
  • 1 foot = 30.48 cm (12 inches)
  • 1 yard = 0.9144 m (3 feet)
  • 1 mile = 1.609 km (5,280 feet)
  • 1 km = 0.6214 miles
  • 1 nautical mile = 1.852 km

Quick Tips

  • A rough rule: km ÷ 1.6 ≈ miles
  • A person 6 ft tall is approximately 183 cm
  • A marathon is exactly 42.195 km (26.219 miles)
  • Earth's equatorial circumference ≈ 40,075 km